When it comes to the Boston Harbor, what goes in...must eventually come out. And as countless criminals and scofflaws have learned, it's usually the Boston Police Department that brings evidence to the surface-figuratively and literally.

Stolen cars, gold jewelry, and guns. Pilfered mail, boat parts, and dead bodies. All have been found in, and recovered by, police from busy Boston Harbor.

"A lot of people think that when they throw something in the water, it's gone," says Boston Police Sgt. Phillip Terenzi, who oversees the department's 42-square-mile harbor patrol. "But just as you would do a crime scene on land, you can do it underwater. With Dive Team capabilities, most anything thrown in the water can be found."

Unlike many seaport cities, which hand off safety and security operations to politically appointed civilian overseers, Boston has a police professional oversee activities at its harbor. Terenzi is the "sah-gent in chahge of da hahbah yoon-it" for Boston Police, the commander of the department's Dive Team, and the city's official harbormaster.

"The opportunity to become part of the Harbor Unit came up in '92, when I was a patrolman," he says. "The main thing (I like about the job) is helping people. That's why I became a cop in the first place. And you're able to do that a lot more in the harbor."

Boston Harbor is a tourist and recreational-boating mecca, attracting tens of thousands of visitors each year. The Port of Boston itself—the largest seaport in Massachusetts—handles about 14 million metric tons of automobiles, petroleum, and other seaborne cargo annually. It employs 9,000 people and supports hundreds of waterfront businesses, including shipyards and private marinas.

Activities in the harbor are monitored by a mulligan stew of law enforcement agencies, including the U.S. Coast Guard, Massachusetts Port Authority, and U.S. Customs and Border Protection. Boston Police Harbor Patrol officers serve as first responders for immediate emergencies and patrol in and around the harbor, including waterways surrounding Boston Logan International Airport.

Back in the day, the unit was seen as an assignment for older officers, because Harbor Patrol officers typically saw less action than street cops. That's no longer the case, says Terenzi, a 27-year-veteran of the Boston Police Department.

Today's Harbor Patrol officers investigate crimes on watercraft and enforce maritime laws promoting safe boating and efficient water traffic patterns for hundreds of ships that use the waterway daily. They enforce Homeland Security protection zones around military vessels and escort tankers carrying potentially hazardous or high-security cargo into the Port of Boston.

"The way the port security is now, it's a lot of work out there," Terenzi says. "These days, you need someone that's motivated, that wants to be out on the water."

Harbor Patrol officers also serve as the primary law enforcement agency for the Boston Harbor Islands, where they handle everything from loud music complaints and petty larcenies to aggravated assaults and the occasional "shots fired" call, which usually turns out to be fireworks.

"The Harbor Unit extends the Boston Police Department's community and neighborhood policing philosophy into yet another 'neighborhood' of the city-otherwise known as the Boston Harbor," says Deputy Superintendent Thomas F. Lee, commander of the Boston Police Department's Special Operations Unit.

The department has provided the Harbor Patrol Unit with a variety of specialized vessels, including the 86-foot "St. Michael," a retired Navy minesweeper; the 41-foot "Due Process," a former Coast Guard utility boat; and two 27-foot, high-speed intercept boats named "Protector" and "Persuader." The pride of the fleet is the "Guardian," a 57-foot Sea Ark used for command-and-control rescue and recovery operations. It is also equipped with state-of-the art navigation, communications and video equipment, and a four-bed medical triage unit.

The Boston Police Dive Team is comprised of 22 officers who work various assignments throughout the department, and are called out for diving or water-rescue operations as needed. Some officers specialize in ice diving and rescues of people or animals that have fallen through the ice. Others specialize in obstructive-area diving, similar to cave diving. Still others specialize in Nitrox scuba diving, which enables officers to extend dive times by using specialized oxygen rebreathing apparatus.

Dive officers have participated in search-and-rescue missions, evidence recovery operations, and underwater searches for drugs or explosives attached to ship hulls, including those of immense cruise liners, cargo ships, and U.S. Navy warships.

"We had done an operation a few years back with the FBI...that ended up being a six-week dive operation, searching for weapons and evidence," says Terenzi, who declined to detail the nature of the investigation. In addition to conducting underwater searches in Worcester, Mass., and East Boston, officers involved in that case also undertook an exhaustive, four-week search beneath a 900-foot pier in Charlestown, Mass.

Working conditions for Dive Team officers are neither pleasant nor safe. In the winter, there is ice to contend with, and even in summer, water temperatures and thick harbor bottom muck can be bitingly cold. For safety reasons, dives must be carefully timed and coordinated to minimize dangers posed by shipping traffic and tides. And the harbor itself is littered with dangerous debris, including broken bottles and cans, sunken boats and automobile parts, and discarded monofilament fishing line that can trap unwary divers in a hazardous, invisible embrace.

In addition to working in open water, dive officers are also called upon to work in claustrophobic confined spaces, such as against the hulls of ships, beneath docks, or inside submerged vessels or vehicles. And while sonar and other scanning equipment can be used to locate larger objects, officers who work dive operations in the harbor itself often have to resort to painstaking hand searches, blinded by swirling silt that dramatically reduces visibility.

"You have to go out and literally touch and feel your way around," Terenzi says. "If you want to search a 900-foot-long parking lot, you can step into that parking lot and do a cursory search in a few minutes. If you're underwater and visibility is zero, it can take weeks."

Bryn Bailer, a former newspaper reporter, is a contributing editor for POLICE. By night, she is a member of the Tucson (Ariz.) Police Department's Communications Division.